Question

Just to get the words clear here in Java.

Primitive types:

This is a declaration right:

int a;//declared but unitialized

Intializations and assignments:

a = 1;//intialization and assignment

a = 2;//this is no longer intialization but still an assignment the 2nd time?

int b = 1;//declaration and intialization = assignment combined?

b = 2;//just assignment because 2nd time?

Class types:

String str;//declaration

str = "some words";//this is also an intialization and assignment?

str = "more words"; //since new object still both intialization and assignment even 2nd time?

Answer 1

The compiler considers a variable initialised when it knows the local variable has been set and can be read without error.

Consider this case, where the compiler cannot determine the a variable has been initialised.

int a;
try {
    a = 1;
    // a is initialised and can be read.
    System.out.println(a); // compiles ok.
} catch (RuntimeException ignored) {
}
// a is not considered initialised as the compiler 
// doesn't know the catch block couldn't be thrown before a is set.
System.out.println(a); // Variable 'a' might not have been initialized

a = 2;
// a is definitely initialised.
System.out.println(a); // compiles ok.